Opaquing agent for vitreous enamels



Patented Oct. E9, 3943 FFICE OPAQUING AGENT FOR VITREOUS ENAMELS Harry C. Kremers, Cleveland Heights, and Lester A. Batenian, East Cleveland, Ohio, assignors to The Harshaw Chemical Company, Elyria,

Ohio, a corporation of Ohio "N Drawing. Application August 20, 1940, Serial No. 353,400

2 Claims. (01.106-312) a This invention relates to ceric oxide opaciflers" and has tor its objects to provide ceric oxide compositions of high opacifying value and a novel and superior process for producing the same.

According to the literature, ceric oxide (CeOz) exists in a yellow and a white form, both of which are said to'have been determined by X-ray examination to be in the cubic system. It has been suggested also that the yellow modification is not actually ceric oxide at all but consists of or contains cerous cerate (CezOr3Ce0z). The oxygen content of Ce2O3 '3CeOz diil'ers from that of 5Ce0: by only about 1.5% so that it is dimcult to establish the composition with certainty. In" any event, it is known that the yellow modification is not suitable for use as an opaquing agent for vitreous enamels whereas the white form is very excellent for that purpose.

Calcination of cerous compounds, g., the hydrate, nitrate or oxalate yield the yellow ceric oxide while calcination oi ceric compounds, e. g.,

the hydrate, nitrate or sulfate, yield the, white be removed from the-quench water washed and dried (or fired for removal of any water of hydration) but these are obvious steps and may not always be followed. The three numbered steps are the significant steps and characterize the process. Cerous compounds also may be employed but in that case they must be calcined under oxidizing conditions. Ceric compounds do not require oxidizing conditions .but we prefer to calcine in an oxidizing atmosphere in either case. Among the cerium compounds which we may use as startingmaterials are eerie and cerous oxides, eerie and cerous hydroxides or hydrates or hydrated oxides, ceric basic nitrate or hydroxy nitrate, cerous carbonate, cerous nitrate, cerous oxalate, cerous and eerie phosphates and cerous and ceric sul-,

fates.

By alkali we'mean one or more substance ii oi the class consisting of alkali metal and alkalin earth metal oxides, hydroxides, carbonates and nitrates. v

The low limit of the extent oi calcination'is placed at the point at which the water has been boiled off because at that point the reaction has proceeded to an extent to result in the-production of a valuable product although in practice we prev fer to calcine to an extent tomomplete or almost complete the reaction. Specifically, we prefer to calcine the mixture from which the water 750 C. to 850 C. The time required to bring the batch to a temperature of 700 C. to 900 C. rangewill meet the time requirements but we prefer a firing cycle involving holding the temperature at the selected maximum or at least within the 700 C. to 900 C. range for from /2 to 1% hours. Raising the temperature above 900 C. does not seem to harm the product but appears not to improve it. We prefer to raise the temperature to 750 C. to 850 C. as rapidly as convenient without using a kiln temperature higher than the desired batch temperature and holding the'batch in that temperature range for hour to 1 /2- hours, desirably about one hour. Normally, the batch will beheld at maximum temperature for a longer time if that temperature is low and for a shorter time if that temperature is high. The desirable thing is that the reaction be broughtto completion.

Normally the calcined mass will be quenched in water butit may be desirable in some cases to employ anacid solution as a quenching medium. For example, it the alkali employed is lime, an acid quenching medium may be the best mode .of separating ceric oxide from calcium oxide.

The optimum proportions of alkali and cerium compound are the stoichiometric proportions theoretically required toproduce; an alkali cerate, e. g. two mols NaOI-I per atom of cerium or one mol Ba(O H)-z per atom of cerium. We believe that such compounds as NazO-CeQ: and 090- CeO: are produced and that they decompose in water leaving CeOa in highly desirable physical state for use as an opacifier in'vitreous enamels. The alkalishould not greatly exceed the optimum proportion on account of the energetic action which occurs on quenching. However, an excess of will be-an admixture oi improved and unim proved material. Ceric oxide is noticeably improved by 25% of the theoretical quantity or alkali and considerably improved by 50% thereof. However, we recommend the use of at least 75%0! the theoretical quantity and, of course,

' prefer to use the stoichiometric ratio. We believe, accordingly, that the essence ofour invention resides in the production of an opaquing I agent which is ceric oxide in the form of an alkali (alkali metal or alkaline earthmetal) create hydrolysis product. However, we donot wish to rest our invention entirely upon theoretical grounds and, accordingly, we describe and claim the process we employ and the product thereof.

A further feature of our invention is the discovery that where the cerium starting material is an oxide or hydrate, the presence of a small material, to mix therewith sodium hydroxide or sodium carbonate in theoretical proportions (plus or minus or mol per cent) to make a sodium cerate and with water to make a thickv slurry, to boil oi! the water andheat further to from 750 C.to 850 C. for from /2 hour to 1 /2 hours, to quench in water, wash'the resulting cerium compound and dry or, optionally, again heat to 700 C. to 900 C. to remove any Physically orchemicallrbound water.

Small quantities of impurities can be tolerated although pure materials are desirable. Of the impurities likely to be present, iron and manganese especially should be kept low, desirably below 0.05% although 0.1% can be tolerated.

The following. specific examples will serve to illustrate the invention:

Example I Approximately 80 parts by weight of NaOH and 172 parts by weight of CeO: (white form) in sufficient water to make a thick slurry were mixed thoroughly and heated until the temperature of the mass was 800 C. 'and held at that temperature for one hour. The mass was then quenched in water whereupon substantially complete decomposition to NaOH and ceric oxide (probably 0 hydrated) occurred. The NaOH was washed out and the ceric oxide or hydrate was heated to 700 C. and held at that temperature for one hour. The resulting ceric oxide was found to have excellent opacifying properties, markedly superior to the ceric oxide starting material.

assaass Example II ofExsmpleI. Thepresenceofphosphateion maybeexpectedtoinereasethereiiectanoennder' favorable conditions one or two per cent. The caustic fusion treatment may be expected to increase thereflectance upto B or! peroentunder favorable conditions.

- Example III Example I was repeated using ceric oxideof the yellow type. The results were equally good.

Thatis, the iinal product was-equal to the final product produced according to Example 1.

Example IV Cerous oxalate was made into a water slurry with'the quantity of NaNO: theoretically required to produce NaaCeOa, ignited, the product washed free from sodium and the ceric compound calcined at 700 C. for one hour. The resulting CeO: was comparable to the product resulting from Example I. v a

Having thus described our invention, what we claim is:

i. A process of producing a ceric oxide of superior opaquing propertiesin vitreous enamels comprising calcining a cerium oxide. NaOH and r a phosphate, the cerium oxide and NaOH being in proportion to form NaaO-CeO: plus or minus 15 mol per cent and the phosphate radical being I present to the extent required to yield phosphate radical to the extentof'from-0;Z%""to 0.8% of the Geo: in the final product, the temperature of calcination being from 700' C. to 900 C. and the time from %'hour to 1% hours, and decomposing the calcination product by the action of water.

2. A process of producing ceric oxide in a form suitable for use as an opaq'uing agent for vitreous enamels includingthe steps of mixing in aqueous medium a cerium compound of the class consisting of ceric and cerous oxides, ceric and cerous hydroxides, hydrates and hydrated oxides, basic ceric nitrate, cerous carbonate, cerous nitrate, cerous oxalate, cerous and ceric phosphates, and

cerous and ceric sulfates,a small amount of phosphate material being included, and an alkaline material of the class consisting of alkali metal and alkaline earth metal oxides, hydroxides, car- 1 bonates and nitrates. calcining the resulting batch at a temperature from 700 C. to 900 C. and then introducing the resulting material into aqueous medium and removing from the resulting aqueous mixture a pigment grade ceric oxide.

- HARRY C. KRMLERB. LESTER A. BATEMAN. 

